Various proposals have been suggested for including a selectively engageable friction clutch within a hydrodynamic torque converter to split torque or for producing an all mechanical drive. Such clutch or lock-up constructions are particularly advantageous in change speed torque converter transmissions for vehicles to increase the transmissions, operating efficiency.
In some clutch devices, split torque usage is limited to small diameter clutches where oil pressure effects are small or on lock-up clutches where differential speeds are low. For example, if there is a shift from an open converter to a split torque drive for cruise operation in a torque converter transmission, the centrifugal pressures on opposite sides of the clutch plate mounted in the hydraulic unit can be unequal and thereby can make the clutch application and release difficult to calibrate.
An object of the present invention is to provide a lock-up clutch arrangement wherein pressure fluid is applied only to one face of the clutch plate and the clutch plate is continuously slipped with respect to a cover portion of a rotary housing of a fluid torque converter to minimize the response time to apply a lock-up force between the clutch plate and the rotating housing either to produce a split torque drive or to produce an all mechanical drive.
Various proposals have been suggested for engaging the friction element of the lock-up in such torque converters U.S. Pat. No. 2,404,657 discloses an arrangement where valves for directing fluid pressure onto the friction plate are activated by centrifugal force. In the arrangement there is no cooling flow once the friction plate is engaged.
U.S. Pat. No. 3,972,400 discloses the use of friction plates run in a fluid. Various groove patterns are suggested for directing flow from the inside diameter of the friction plates to the outside diameter thereof. The provision of grooves across the entire width of the facing would leak in a torque converter application where it is desirable to seal the activating fluid from the outboard face of a piston plate for carrying friction material that is engageable with the front cover of a rotatable housing of a torque converter for producing a desired lock-up therein.
U.S. Pat. No. 4,445,599 discloses a torque converter lock-up system which provides cooling flow once the lock-up is engaged. In this arrangement, passages are provided through a metal piston plate to cool the locked up clutch rather than providing for flow through grooves in the friction material. The fluid flow in the -599 arrangement, again, will provide a leakage path for flow of the pressurizing fluid from the unit during lock-up.
U.S. Pat. No. 4,462,492 is like the arrangement in the U.S. Pat. No. 4,445,99. Again, the coolant arrangement is through a piston plate material, rather than the friction material and the path again constitutes a leakage path for the energizing fluid.
U.S. Pat. No. 4,638,897 discloses a lock-up plate that has a notch in friction material and a hole through an adjacent steel plate for the friction material. The hole through the adjacent steel plate is utilized to define a leakage path which is used in conjunction with the cover plate of the torque converter to modulate pressure across the plate. The hole is not used for cooling a frictional running surface which continuously slips across the cover of a rotating housing of a torque converter.